Xray Magnetic Circular Dichroism Investigation in Ferromagnetic Semiconductors Khashayar Khazen Condensed Matter National Lab-IPM
IPM School of Physics School of Nano Condensed Matter National Lab Technology: Energy production & storage Information technology Quantum electronics Construction materials Catalysts Novel coatings High-tech textiles Water desalination Medical treatments Novel 2D materials (Coordination of 32 international projects) Fundamental science: Plasmonics Surface charge transfer Mechanical properties Liquid crystals Valleytronics France: CNRS, Sorbonnes Universities, ESPCI, Ecole Polytechnique, Universite Paris Sud, Institut Curie Denmark: European Centre for Electron Nanoscopy Irland: Trinity College Dublin Germany: University of Paderborn Netherlands: Groningen University Belgium: University of Antwerp Australia: IPIR, ISEM USA: Massachusetts Institute of Technology China: North-West university
Ferromagnetic semiconductors Unified Information Storage and Processing Unit (III-V semiconductors doped by transition metals) Compatibility with currently used microelectronic technology Magnetism control: Electrical control via charge density and wave function Optical control via spin-orbit coupling between photon angular momentum and carrier spins Structural control via strain
How to make GaAs ferromagnetic? P-type conductivity: Mn 2+ acceptor + h Magnetic ions: Mn 2+ S=5/2 J Mn-Mn =0.23 mev Magnetic coupling: Zener kinetic exchange T c α J 2 pd.x Mn.p 1/3 Intrinsic ferromagnetic phase with highest T C ~190K Intrinsic limit of Curie temperature in GaMnAs J Mn-h = -54 mevnm 3 Phys. Rev. B, 81, 255201 (2010) Thin solid films 519, 8212 (2010) K. Khazen PhD thesis
Room Temperature Ferromagnetic Ga 1-x Mn x As? External control of magnetic order: Interlayer coupling 2nm Maccherozzi et al, PRL 2008
Room Temperature Ferromagnetic Ga 1-x Mn x As? External control of magnetic order: Interlayer coupling 2nm Maccherozzi et al, PRL 2008 Detailed magnetic properties investigations: Magneic resonance Magnetometry XPS X-ray diffraction and reflection Ion beam analysis Spin polarized neutron reflectivity XMCD
Room temperature Ferromagnetic Ga 1-x Mn x As? A. Two step layer growth LPN-Alcatel, Simon Fraser Univ
Room temperature Ferromagnetic Ga 1-x Mn x As? A. Two step layer growth LPN-Alcatel, Simon Fraser Univ Landau-Lifshtiz: Ferromagnetic Resonance Spectroscopy 15070905M.dat Fe/GaMnAs inplane 145 lu 4K,P= 20dB,G=7.96E+5,B= 10G,Freq= 94.707207 15070906M.dat Fe/GaMnAs inplane 100 lu 4K,P= 20dB,G=7.96E+5,B= 10G,Freq= 94.700379 15070908M.dat Fe/GaMnAs inplane 55 lu 4K,P= 20dB,G=7.96E+5,B= 10G,Freq= 94.705696 EPR Signal (arb.u.) 240000 1-10 100 110 220000 200000 180000 160000 140000 120000 100000 80000 60000 0 500 1000 1500 2000 2500 Magnetic Field (G) T=4K 5000 4000 3000 2000 1000 0-1000 27070901M.dat GaMnAs/Fe,Bret sample,out-of-plane,144dg,0dg de inplane,294k,p= 20dB,G=5.E+3,B= 10G,Freq= 9.34732 27070903M.dat GaMnAs/Fe,Bret sample,out-of-plane,144dg,0dg de inplane,294k,p= 20dB,G=5.E+5,B= 10G,Freq= 9.34741-2000 0 1000 2000 3000 4000 5000 Magnetic Field(G) T=300K H eff K anisotropy Polycrystalline Fe and single crystalline GaMnAs Presence of second phase superparamagnetic particles in the interface
Room temperature Ferromagnetic Ga 1-x Mn x As? B. One step layer growth Nottingham RHEED XRR 60 50 40 SLD (10^-6 A -2) 30 20 10 Epitaxial growth of Fe over GaMnAs 0 1 2-4 -2 0 2 4 6 8 z (nm)
Room temperature Ferromagnetic Ga 1-x Mn x As? B. One step layer growth Nottingham RHEED XRR 60 50 40 SLD (10^-6 A -2) 30 20 10 Epitaxial growth of Fe over GaMnAs 0 1 2-4 -2 0 2 4 6 8 z (nm) B//[001] 0 40K 240000 220000 110 100 1-10 EPR Signal (arb.u.) -2000-4000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 Magnetic Field (G) 35K 30K 25K 20K 15K 10K 4K EPR Signal (arb.u.) 200000 180000 160000 140000 120000 100000 Mn509 T=300K 80000 4500 5000 5500 6000 6500 7000 7500 8000 Magnetic Field (G) No second phase formation The interface magnetism and its origin can not be studied via FMR
XMCD spectroscopy Sharp increases in Xray Absorption coefficient: Absorption edges Transferring low energy bound electrons to empty states just above the Fermi energy Element specific Process
XMCD spectroscopy Circularly polarized photons Angular momentum transfer to electrons Attenuation coefficient dependence on the relative orientation of the photon helicity and sample magnetization
XMCD spectroscopy Circularly polarized photons Angular momentum transfer to electrons Attenuation coefficient dependence on the relative orientation of the photon helicity and sample magnetization Allowed transitions l = ±1 and m = ±1 and ms = 0
XMCD spectroscopy Circularly polarized photons Angular momentum transfer to electrons Attenuation coefficient dependence on the relative orientation of the photon helicity and sample magnetization Allowed transitions Difference in right and left-handed polarized XA l = ±1 and m = ±1 and ms = 0
XMCD spectroscopy Main detection techniques: (i) Auger decay: an intermediate electron drops into the hole and the liberated energy results in the ejection of another electron (ii) Fluorescent decay: where the photoelectron generated by the absorption event recombines with the hole left behind re-emitting an x-ray photon
XMCD spectroscopy Main detection techniques: (i) Auger decay: an intermediate electron drops into the hole and the liberated energy results in the ejection of another electron (ii) Fluorescent decay: where the photoelectron generated by the absorption event recombines with the hole left behind re-emitting an x-ray photon As each detected particle originates from different spatial region Attenuation length of Xray, for (Ga,Mn)As=561 nm Escape depth of electrons =2.9nm Depth resolution
XMCD at the Mn L2,3 edge Diamond Light Source, I06 beamline Experiments led by Kevin Edmonds James Heigh and Peter Wadely PhD thesis
XMCD at the Mn L2,3 edge Diamond Light Source, I06 beamline Conditions: Room temperature measurements TEY detection A small but clear Mn-related peak observed at room temperature Comparison of the peak with reference, Mn, FeMn, MnAS, etc, revealed that it is a localized Mn 2+ localized state
XMCD at the Mn L2,3 edge Diamond Light Source, I06 beamline Conditions: T=2K measurements TEY and FY detection Attenuation Anti-parallel alignment of the Mn moment at H=0 Signal from the surface shows frustration Proposed model: proximity polarisation of the Mn ions near to the Fe layer thickness of the strongly coupled layer of x = 0.9 nm K. Olejnik et al, PRB 2010
Take-home message Element-resolved character, nano/micro spatial resolution, and possibility to distinguish spin/orbital contributions important role in novel magnetic system development But, it should be noted that using synchrotron based techniques should be justified. Not limited to conventional and classic techniques available at the beamlines. much more to be explored!